1. Field of the Invention
The present invention relates to a process cartridge accommodating a plurality of process units for image formation therein and an image forming apparatus using the same.
2. Description of the Background Art
It is a common practice with an electro photographic image forming apparatus to form a latent image on a photoconductive element or image carrier, develop the latent image to thereby produce a corresponding toner image, and transfer the toner image to a paper sheet or similar recording medium. Such an image forming apparatus is implemented as a copier, a printer, a facsimile apparatus or a multifunction machine having at least two of the functions available therewith by way of example, as taught in, e.g., Japanese Patent Laid-Open Publication No. 2002-6679 (page 3 and FIG. 1).
The image forming apparatus of the type described is provided with a single photoconductive element assigned to a single color or a plurality of photoconductive elements each being assigned to one of a plurality of different colors. The image forming apparatus with a single photoconductive element may be implemented as, e.g., a monochromatic copier while the image forming apparatus with a plurality of photoconductive elements may be implemented as, e.g., a color copier.
One of conventional methods available for forming a full-color image forms toner images of different colors on respective photoconductive elements with developers complementary to separated colors, and sequentially transfers the toner images to a paper sheet or similar recording medium one above the other. Another conventional method sequentially transfers the toner images from the photoconductive elements to an intermediate image transfer body one above the other and then transfers the resulting full-color image from the intermediate image transfer body to a paper sheet.
A tandem image forming apparatus taught in, e.g., Japanese Patent Laid-Open Publication No. 2003-316107 (column [0010]) is another full-color image forming apparatus and has a plurality of photoconductive elements arranged side by side along an intermediate image transfer belt. To reduce the overall size of the tandem image forming apparatus, Japanese Patent Laid-Open Publication No. 2003-202728, for example, proposes to arrange image forming stations each being assigned to a particular color and image transferring devices facing them in an inclined position.
As for a tandem image forming apparatus, Laid-Open Publication No. 2003-216107 mentioned above further discloses process cartridges mounted on the apparatus each accommodating a photoconductive element assigned to a particular color and various process units for image formation.
Generally, when a process cartridge includes a photoconductive element and a developing device for developing a latent image formed on the photoconductive element, it is likely that a developer stored in the developing device accidentally leaks to the outside due to vibration during transport or installation. In light of this, the process cartridge is sometimes dealt with as unit packed independently of an image forming apparatus.
When the process cartridge in use on the image forming apparatus must be replace because of the limited life of any part thereof or when a space must be temporarily provided within the image forming apparatus for maintenance or inspection, the process cartridge is sometimes dismounted from the apparatus and then placed on a desk or similar horizontal surface.
On the other hand, some developer is stored in the developing device included in the process cartridge at the beginning, so that the developer can be rapidly fed as soon as the process unit is mounted to the image forming apparatus. In this case, the developer is often implemented as a two-ingredient type developer, i.e., a toner and carrier mixture.
A prerequisite with a toner and carrier mixture is to deposit a preselected amount of charge on toner grains by mixing and agitating toner grains and carrier grains together. To meet this prerequisite, Laid-Open Publication Nos. 2002-6679 and 2003-202728 mentioned earlier each propose a particular configuration wherein a pair of screws for conveyance and a sleeve for development are accommodated in respective spaces. The toner and carrier grains are electrified by agitation in the space accommodating the screws. On the other hand, when the process cartridge is new, some amount of developer charged beforehand is stored.
In any case, in a new process cartridge, a seal member separates the above two spaces assigned to the screws and sleeve, respectively, in order to prevent the developer in the former from accidentally entering the latter and then leaking to the outside via gaps between exposed part of the sleeve, which faces a photoconductive element, and the inner periphery of the space accommodating it. After the new process cartridge has been mounted to an image forming apparatus, the seal member is pulled out to provide communication between the two spaces for thereby allowing the developer to be fed to the sleeve by the screws.
A process cartridge wherein a developing sleeve is positioned above a pair of screws may be arranged in matching relation to the inclination of an image transferring device, as taught in, e.g., Laid-Open Publication Nos. 2002-2279 and 2003-202728. More specifically, when a new process cartridge or a process cartridge dismounted from an image forming apparatus is placed on a desk or similar flat surface, it is put in the same position as when mounted on the apparatus, i.e., the sleeve is so positioned as to feed the developer to a photoconductive element while facing it. It is therefore likely that the developer deposited on the sleeve accidentally leaks to the outside of the process cartridge or that, when the space accommodating the sleeve is not sealed, the developer enters the space adjoining the sleeve and also leak to the outside at the position where sleeve is exposed.
In light of the above, it is necessary to prepare a special base or similar structural part configured to support the process cartridge such that the exposed portion of the sleeve is not positioned in the same orientation as when mounted on the apparatus. However, it is difficult for the user of the apparatus to prepare such a special base, forcing the user to rely on a serviceman call.